Diesters containing adamantane nuclei



United States Patent 3,398,165 DIESTERS CONTAINING ADAMANTANE NUCLEI IrlN. Duling, West Chester, and Abraham Schneider, Over-brook Hills, Pa.,assignors to Sun Oil Company, Philadelphia, Pa., a corporation of NewJersey N0 Drawing. Filed Mar. 2, 1966, Ser. No. 531,059 13 Claims. (Cl.260-410) This invention relates to novel diesters containing one or twoadamantane nuclei per molecule. Each adamantane nucleus contains notmore than one unsubstituted bridgehead carbon atom or in other words hasnot more than one tertiary hydrogen atom attached thereto. The diestersare either oily liquids or waxy solids. They are characterized by goodhydrolytic stability, oxidative stability and thermal stability and haveparticular utility as lubricants or as components in lubricating oil andgrease compositions.

The diesters of the present invention comprise two types as follows:

(I) Diesters of alkyl-substituted adamantane 1,3-diols with alkanoic orcycloalkanoic acids.

(II) Diesters of alkyl-substituted adamantane l-mono- 01s withalkanedioic or cycloalkanedioic acids.

These two types of diesters are represented by structural formulas ashereinafter shown. They are both characterized as being derived from theesterification of the specified monoor di-acids by alcohols in which thehydroxy group or groups are located at bridgehead positions of theadamantane nucleus.

The use of certain types of diesters as synthetic lubricating oils andgreases for special applications is well known and is described, forexample, in Synthetic Lubricants by Gunderson and Hart (ReinholdPublishing Corp, 1962), pages 39-43 and 151-245. These synthetic esterlubricants comprise di-esters made from aliphatic monoalcohols andaliphatic dibasic acids such as glutaric, adipic, azelaic and sebacicacids, as well as the reverse type of diesters made from glycols andaliphatic monocarboxylic acids. Those made from the aliphatic monoolsand diacids have been used widely as aircraft lubricants for turbopropand turbojet engines, usually being formulated with suitable additivesto meet United States Military Specification MlL-L-7808. Lubricants forthis purpose are required to have low temperature fluiditycharacteristics as well as good stability at high temperature operatingconditions. The specific diester used perhaps most widely for gasturbine engine lubrication is the di(2-ethylhexyl)sebacate. Besidesbeing used for aircraft engine lubrication, synthetic diesters have alsobeen employed as gear oils, instrument oils, machine gun lubricants,hydraulic fluids and greases.

In the prior art monoesters of l-adamantane carboxylic acid and severalaliphatic alcohols have been prepared and testified for suitability aslubricating oils. This Work has been described by Spengler et al., Erdolund Kohle- 'Erdgas-Petrochemie, vol. 15, pages 702-707 (September,1962). The alcohols used ranged from propanol to tetradecanol. Themonoester products were oils but they did not prove to be attractive asspecial lubricants. Each molecule of these esters contained threeunsubstituted bridgehead carbon atoms in the adamantane nucleus or,

in other words, three tertiary hydrogen atoms which provide relativelyreactive sites in the molecule. While their thermal stability wasconsidered good, the resistance to oxidation in the presence of metalswas reported to be poor as also was the lubricating quality of theesters. These authors also reported preparing a diester of 1- adamantanecarboxylic acid and hexamethylene-l,6-glycol but this product was a highmelting solid (M.P.=l01 C.) rather than an oil.

The present invention is directed to diesters containing either one ortwo adamantane nuclei and in which each ester group is the reverse ofthat in the prior art referred to above. In other words the adamantanenucleus (A) is attached to an oxygen atom of the carboxyl group in tlnsfashion,

rather than to the carbon atom in .the linkage The present structuralarrangement,

resulting from the adamantane-derived reactant being an alcohol insteadof an acid, imparts greater stability to the ester product for reasonsas hereinafter explained.

The diester products provided by the present invention conform instructure either to Formula I or Formula II as follows:

R3-C-O o-c-R H II R o-c-R -c-o R In these formulas the R groups are asfollows:

R a radical having 0-20 carbon atoms selected from the class ofhydrogen, alkyl and cycloalkyl,

R and R alkyl or cycloalkyl radicals having 1-20 carbon atoms each,

R an alkylene or cycloalkylene radical having 1-20 carbon atoms.

It should be noted that of the specified substituents at the bridgeheadpositions of the adamantane nuclei only R can be a hydrogen atom. Henceonly one tertiary hydrogen atom can be attached to each adamantanenucleus. Embodiments of the invention which may often be preferred foreither type of diester will have an alkyl substituent at the R positionand hence will contain'no tertiary hydrogen on the adamantane nucleus.For both types of diesters it is usually preferable that the variousbridgehead substituents (R R and, in Formula 11, R be methyl or ethylgroups or both, as the substituted adamantanes corresponding thereto canbe more readily obtained as starting material for preparing thecorresponding products in accordance with the invention.

Both of the above-specified types of diesters have high stabilitiesagainst thermal and oxidative degradation and good hydrolytic stability.As compared to the prior art esters mentioned above, the presentdiesters have better thermal stability by virtue of the fact that adouble bond cannot form in an adamantane nucleus. Awell knowndecomposition route for conventional types of esters depends upon theirability, under appropriate conditions, to transfer a hydrogen atom fromthe beta position of the alcohol-derived moiety in the following manner:

This decomposition results, as shown, in the conversion of the esterinto an acid and an olefin. The occurrence of this in a lubricant underconditions of use, of course, would be highly undesirable. While theprior art esters can undergo this type of decomposition at hightemperature, the present ester cannot as this would require theformation of a double bond in the adamantane nucleus which will notoccur. In contrast the reverse type of esters made from l-adamantanecarboxylic acid and an aliphatic alcohol or glycol can undergo this typeof thermal decomposition.

Another reason for the overall better stability of the present productsas compared to the prior art esters made from 1 adamantane carboxylicacid is the fact that the present products have at most only onetertiary hydrogen attached at each adamantane nucleus and preferably mayhave none. In comparison the prior art esters have three bridgeheadtertiary hydrogen sites on each adamantane nucleus. These are reactivesites constituting spots in the molecule where oxidation and peroxideformation can occur.

Still another reason for the better stability of the present products isthat the ester structure represented by will less readily undergohydrolysis under non-acidic conditions than the reverse structure Sincecontamination of the lubricant by water may occur in some lubricationsystems, this improved hydrolytic stability provides still anotherdesirable stability feature of the present products.

As starting material for preparing the diesters, bridgehead mono-, diortri-alkylated adamantanes corresponding to the desired alkyl orcycloalkyl adamantane moiety of the product can be used. For making theproducts of Formula I only the monoand di-alkylated ada- I! OH ER CCImantanes can be used, whereas for those of Formula 11 trialkylatedadamantanes can also be employed. While the number of carbon atoms ineach alkyl or cycloalkyl group can vary widely ranging say up to 20, itis usually preferable that the R groups be methyl and/or ethyl since theparent hydrocarbons corresponding thereto are more readily obtainable.Thus l-ethyladamantane, 1,3-dimethyladamantane,l-ethy1-3-methyladamantane, 1,3,5- trimethyladamantane and1,3-dimethyl-5-ethyladamantane can be prepared by aluminum halidecatalyzed isomerization of C C tricyclic perhydroaromatics, as disclosedby Schneider et al., JACS, vol. 86, pp. 5365-5367. Higher alkyl orcycloalkyl groups can be substituted on the adamantane nucleus by aWurtz snythesis involving reacting bridgehead chloro or bromoadamantanes with alkali metal alkyls or cycloalkyls in the mannerdisclosed in the aforesaid Spengler et al. reference. The alkylatedadamantanes can, for the present purpose, have either nonbranched orbranched alkyl groups and can have one or more cycloalkyl radicals inthe alkylation moiety with the total number of carbon atoms in each Rgroup ranging up to twenty. Preferably the R groups contain no tertiaryhydrogen atoms.

The starting alkylated adamantane hydrocarbon is first converted to a1,3-diol if esters according to Formula I are desired, or to a l-monoolif Formula II products are the kind to be prepared. One manner ofeffecting such conversions is by air oxidation of the parenthydrocarbons at, for example, 160 C. in the presence of a metal saltoxidation catalyst, as disclosed in Schneider United States applicationsSer. No. 395,557, now U.S. Patent 3,356,740 and Ser. No. 395,580, nowUS. Patent 3,356,- 741 each filed Sept. 10, 1964. In the oxidationmonools form first and these will subsequently convert to diols if thereaction is allowed to continue sufficiently. Some amounts of ketonesare also formed during the oxidation. Production of the monools can bemaximized by stopping the oxidation before conversion has been reached,while production of diols can be maximized by oxidizing to higherconversion levels.

Another way of preparing either l-monools or 1,3-diols of thealkyladamantanes is by reacting the latter with an acetic acid solutionof chromic acid, as disclosed in Moore United States application Ser.No. 421,614, filed Dec. 28, 1964, now abandoned. By using a relativelylow mole ratio of Cr to hydrocarbon such as 3 :2 good yields of themonool can be obtained, whereas using a higher ratio such as 6:1 resultsin good yields of the diol.

The preparation of diesters utilizing these bridgehead monools or diolsof alkyladamantanes is not as readily accomplished as When aliphaticalcohols or glycols are employed. Attachment of the hydroxyl group at abridgehead carbon of the adamantane nucleus makes the group relativelyinactive. This is especially true when two bridgehead hydroxyl groupsare attached to the nucleus. Hence many of the known methods ofesterification may not be suitable for making products of the presentinvention or at least for obtaining these products in good yield. Forexample, conventional esterification of the l-monools or 1,3-diols withaliphatic diacids or monoacids by means of an acidic catalyst generallyis not a good way of preparing these diester products.

A preferred procedure for making the diesters is by reacting thehydroxy-containing adamantane compound with aliphatic or cycloaliphaticacid chlorides. Thus, for producing the Type I diesters, the procedureinvolves the following reaction:

This reaction takes place too slowly at room temperature and hence anelevated temperature should be employed, e.g., 100-150 C. A solvent suchas pyridine can be used so that the hydrogen chloride will beneutralized as it is formed. While this is not essential, it isadvantageous for inhibiting side reaction particularly in cases where Ris a hydrogen atom.

The preferred esterification procedure for making Type II diestersinvolves reaction as follows:

This esterification reaction takes place more readily than that of thepreceding equation and can be carried out at room temperature simply bymixing the two reactants. The reaction is exothermic and hence it isdesirable to add the monool slowly to the alkane dioyl chloride whilestirring the mixture. Again a solvent such as pyridine can be used toavoid side reaction and is particularly desirable in case R is ahydrogen rather than an alkyl substituent.

In carrying out the first shown esterification whereindihydroxyadamantanes are used, stoichiometric proportions of thereactants can be used but it is generally preferable to employ an excessof the acyl chloride. An excess of the diol would lead to the formationof hydroxy monoesters which should be avoided. An excess of the acylchloride, however, helps to insure complete esterification of the diols.Furthermore the excess acyl chloride can be readily removed from thereaction product by treatment with an aqueous solution of sodiumcarbonate or other alkali, whereas any excess of the hydroxy-containingcomponent cannot be removed in this manner. Generally a molar ratio ofacyl chloride to the dihydroxyadamantane reactant in the range of 2:1 to:1 will be used in carrying out this reaction.

In effecting the other esterification in which monohydroxyadamantanesare employed, the use of a stoichiometric excess of the alcohol helps toinsure complete esterification of the alkane dioyl chloride. Howeverremoval of the excess alcohol is not readily effected, as this requiresthe use of such separation procedures as chromatography, distillationand/or fractional crystallization. It is generally desirable to use atleast a stoichiometric amount of the dioyl chloride and preferably asmall excess. For example, the molar ratio of the dioyl chloride to themonool may be in the range of 0.5 :l to 0.7: 1. Any resulting half-estercan be removed by washing the product with aqueous sodium carbonate.

After the esterification reaction has been completed, any conventionalor suitable procedure can be used for working up the product. Themixture can be diluted with a solvent such as ether, pentane or benzeneand then washed with aqueous sodium carbonate solution or other mildalkali to remove any acid chlorides. The diester product can berecovered in relatively pure form by distillation and/ orchromatography. In cases where highly pure product is desired,hydrogenation using Raney nickel catalyst (which does not affect theester group) and contact with decolorizing adsorbents can be utilized.The diesters of both types when highly pure are colorless, while theless pure products usually have a pale yellow color. These products aregenerally viscous oils, except that increasing the sizes of the variousR groups in the molecules causes the produces to become waxy solids andparticularly so when the R group are unbranched chains. Preferredproducts of the invention wherein the R groups attached to theadamantane nuclei are methyl and/or ethyl are oils at ordinarytemperature.

For preparing Type I diesters the acyl chlorides of any alkyl orcycloalkyl monocarboxylic acids having 2-21 carbon atoms are suitablefor contributing the moieties to the molecules, and fatty acids areinexpensive sources of this component. Acyl chlorides having 6-12 carbonatoms and a straight chain R group are preferred for making lubricantoils. Specific examples are the chlorides corresponding to the followingacids: caproic, nheptylic, caprylic, pelargonic, capric, n-undecylic andlauric. However, lower and higher members can also be used such as thechlorides corresponding to the following carboxylic acids: acetic,propionic, butyric, isovaleric, myristic, palmitic, stearic, arachidicand the like. Also chlorides corresponding to acids containing naphthenerings can be used, for example, corresponding to cyclohexane carboxylicacid or Decalin carboxylic acids.

For the Type II diesters the dioyl chlorides of any alkylene orcycloalkylene dicarboxylic acids having 3-22 carbon atoms can beemployed as the source of the o 0 labillinkage. Those corresponding tostraight chain diacids having 6-12 atoms are preferred for makinglubricant oils namely, the following diterminal diacids: adipic,pimelic, suberic, azelaic, sebacic, undecanedioic and dodecanedioic.However, dichlorides of diacids having less or more carbon atoms alsocan be used including those of malonic, succinic and glutaric acids, asalso can the dichlorides of diacids containing naphthene rings such ascyclohexane dicarboxylic acids or Decalin dicarboxylic acids.

Any of the foregoing acid chlorides can be made from the correspondingmonoacid or diacid by reacting the same in known manner with suitablechloride reagents such as phosgene, thionyl chloride, oxalyl chloride,PCl or PCl The following examples are specific illustrations of theinvention:

Example 1.-Preparation of 1,3-(5,7-dimethyl)adamantyl dipelargonate Thisexample shows preparation of the above designated Type I diester frompelargonic acid (R =8 carbons) and 1,3-dihydr0xy-5,7-dimethyladamantane.Oxalyl chloride was used to convert the pelargonic acid to its acylchloride. Specifically, g. of oxalyl chloride were slowly added to g. ofpelargonic acid and the mixture was refluxed for 2 hours. Excess oxalylchloride was removed under aspirator vacuum at room temperature. Theresulting acid chloride was heated to 105-1 10 C. and 70 g. of1,3-dihydroxy-5,7-dimethyladamantane were cautiously added in smallportions to the well stirred mixture. The oil was then stirred andheated at C. for one-half hour to complete the reaction. After this asolution of 50 g. sodium carbonate in 300 ml. water was added and themixture was stirred for 2-3 days, then diluted to 1200 ml. with waterand extracted with 500 ml. ether. The ether layer was washed twice withsodium chloride solution, stirred with anhydrous magnesium sulfate andcharcoal, and filtered to give a light yellow solution. Evaporation ofthe ether gave g. of the 1,3-(5,7-dimethyl)adamantyl dipelargonate.Identification was accomplished by infrared, NMR, and mass spectra ofthe broad VPC peak. The diester product was a pale yellow oil and itsproperties are listed in Table 1 infra.

Examples 2-5 For Examples 2, 3, 4 and 5 other Type I diesters were madefrom 1,3-dihydroxy-5,7-dimethyladamantane insubadamantyl)dodecancdicarboxylate. This oil had prop erties as shown inTable 2 infra.

Examples 7-8 In these examples two other Type II diesters were preparedin substantially the same manner as described in TABLE 1.PROPERTIES OFTYPE I DIESTERS Density, R.I., Kv. at Kv. at ASTM Glass Melting AcidUsed No. of O g./l. at 20 0. 100 F., 210 F., D-567, Transi- Point,

1n R 20 C. es. es. V.I. tion Temp. OJ

1 T and M.P. obtained by diflerential thermal analysis. 2 At C.

3 None. 4 Higher glass transition temperature for the dilaurate due toerystallluity.

The data in Table 1 show that a variety of Type I diester oils can bemade of different viscosities and varying widely in viscosity index.Some of the oils will have Example 6 except that the diacids used were,respectively, adipic acid (R =4 C) and azelaic acid (R =7 C). Theseproducts likewise were oils having the properties relatively high V.I.values, as shown by the dipelargonate 25 shown in Table 2.

TABLE 2.-PROPERTIES OF TYPE II DIESTERS Density, R.I., ASTM GlassMelting Dlaeld Used N o. of G g./l. at 20 0. EV. at 100 Kmat 210 D-567,Transition Point,

in R4 20 0. F., es. F., cs. V.I. Temp. 0.

D ('IQ, (3.

Adlpie 4 32. 6 9. 76 62 Azelaic 7 1. 036 1 4977 245.1 15.3 -64Dodeeanedioie 10 1.008 1 4944 370 6 23.6 88 67 2 None.

Example 6.Preparation of bis-(3,5-dimethyladamantyl)dodecanedicarboxylate In this example the above-specified Type IIdiester was prepared from the diterminal diacid, dodecanedicarboxylicacid (R =l0 C), and 1,3-dihydroxy-5,7-dimethyladamantane. The diacid wasfirst convented to the alkane dioyl chloride by means of oxalylchloride. Specifically 10 ml. of oxalyl chloride were added dropwise to5. g. of the diacid in a 100 ml. flask fitted with a reflux condenserand a dropping funnel. Vigorous reaction and evolution of gas occurred.The mixture was gently reiluxed tior two hours and allowed to cool toroom temperature. Excess oxalyl chloride was removed at room temperatureby maintaining the flask under aspirator vacuum for two hours. Thenl-hydroxy-3,S-dimethyladamantane (7.6 g.) was added in three portions,an aspirator vacuum being maintained between additions to facilitateremoval of by-product 'HCl. The mixture was stirred for one-half hourwith gentle heating, then cautiously added to 10% sodium carbonatesolution (500 ml.). The mixture was stirred overnight and extractedtwice with a total of 500 ml. ether. The combined ether layers werewashed three times with water (sodium chloride sometimes was added tobreak up an emulsion), then stirred with anhydrous magnesium sulfate anddecolo-rizing carbon. Filtration and evaporation of the ether gave 11.5g. of a clear yellow oil. This oil was chromatographed on alumina.Combination of center fractions gave 6.5 g. of a colorless viscous oilafter removal of the elution solvent (5% ether in hexane).Characterization of the single broad VPC peak by infrared, NMR and massspectra identified the product as bis-(3,5-dimethyl- As shown in Table 2the three representative oils of Type II were more viscous than those ofTable I. The data for both types of diester's show that V.I. increasesas the length of the linear chains derived from the aliphatic acidincreases.

Products of the invention have better low temperature properties thanwould be predicted from the A.S.T.M. viscosity-temperature slope betweenF. and 210 F. This is shown, for example, by data listed in Table 3 forthe dipelargonate product of Example 1. Table 3 shows measured values ofkinematic viscosities at various temperatures compared with valuespredicted from the A.S.T.M. slope. It also shows flash point, T and pourpoint values for this product.

TABLE 3.PROPERTIES OF DIPELARGONATE EXAMPLE 1 Predicted MeasuredViscosity properties:

K at 500 Kv. at 210 F- 7. O5 Ky. at 100 F. 54.1 Ky. at 0 F. 2, 924 Kv.at -30 22, 076 Pour point, F. 90 O F Flash point, F 480 As shown here,viscosities at temperature below 0 F. are considerably less than thevalues that would be predicted from the A.S.T.M. slope.

Example 9' solution (one liter). The mixture was filtered throughdiatomaceous earth, pentane being used to wash the oil therefrom. Thepentane layer was separated from the green aqueous layer and washedthree times with water. Most of the pentane was stripped OE andanhydrous sodium carbonate added to the oil to make a thick paste. Thiswas maintained for 2 hours at 70 C. under nitrogen. The sodium carbonatewas filtered from the oil and washed with pentane. Alumina (5 g.) wasadded to the pentane solution and the mixture was stirred two hours at70 C. under nitrogen. The pentane was stripped oif and the oil wasdistilled. The first 5% and the last 7% of distillate were discarded. Asmall amount of dark residue was obtained and also discarded. Theproduct boiled at 212.5 C. at .12 mm. Hg. The oil was filtered through a0.8 fiberglass filter covered with /2 inch of alumina. The resultingclear, colorless product had a faint pleasant ester odor, acid number .2and iodine number 1.

The highly purified dipelargonate product was subjected to two kinds ofstability tests. One was a thermal stability test involving subjectingthe oil in a nitrogen atmosphere to 600 F. for 6 hours. For comparison,the conventional ester lubricant, di (2 ethylhexyl)sebacate, was alsotested by this procedure. The other was a bench scale test for corrosionand oxidation stability substantially like that described in WAD Tech.Rep. 60-794 (Wright Air Development Center). This involved contacting aml. sample in the presence of a copper washer for 24 hours at 400 F.with air at a rate of 20 l./hr. Again for comparison, di 2ethylhexyl)sebacate was tested in the same manner. For these corrosionand oxidation stability tests both oils contained added inhibitors inconventional amounts.

TABLE 4.THERMAL STABILITY (600 F.) TESTS The foregoing specific examplesare illustrative of the two types of diester products within the scopeof the invention. Many other specific examples conforming to eitherFormula I or Formula 11 could be enumerated. When any one of the Rgroups in the molecule is straight chain and becomes long enough, theproduct tends to be a waxy solid instead of an oil. However these waxescan also be used for lubricant purposes, for example, as components ofgreases.

We claim:

1. A diester having 1-2 adamantane nuclei and corresponding to one ofthe following formulas:

E? 1 -0-0 o-c-R 1 1. 0 o R n II R 3 o-c am-c-o 3 an wherein R is aradical having 0-20 carbon atoms selected from the group consisting ofhydrogen, alkyl and cycloalkyl, R and R are alkyl or cycloalkyl radicalshaving 1-20 carbon atoms, and R is an alkylene or cycloalkene radicalhaving 1-20 carbon atoms.

2. A diester according to claim 1 corresponding to Formula I.

3. A diester according to claim 2 wherein R and R have 1-2 carbon atomseach.

1,8-(5,7-dimethyl)- adamantyl dipelargonate di-(2-ethy1hexyl)- sebacate1 Mainly solid.

4. A diester according to claim 3 wherein R is an alkyl group having5-41 carbon atoms.

5. A diester according to claim 2 which is a diester Results of thecomparative corrosion and oxidation of1,3-dihydroxy-5,7-dimethyladamantane and an alkanoic stability tests areset forth in Table 5.

acid.

TABLE 5.CORROSION AND OXIDATION STABILITY TESTS1,3-(5,7-dimethyD-adamantyl di-(2-ethylhexyl) dipelargonate (inhibited)sebacate (inhibited) KV. at F.:

Before test After test Percent increase.

Percent increase Evaporation Loss, wt. percent Appearance after testPercent Insolubles Efiect on Copper:

Weight loss, mgJsq. cm

A.S.T.M. D-l30 rating Brown; no precipitation.

2 Brown; moderate precipitation: 3 S1. tarnish.

l Corrosion.

6. A diester according to claim 5 wherein said alkanoic acid is selectedfrom the group consisting of caproic, n-heptylic, caprylic, pelargonic,capric, undecyclic and lauric acids.

7. A diester according to claim 1 corresponding to 13. A diesteraccording to claim 12 wherein said al- Formula II. kanedioic acid isselected from the group consisting of 8. A diester according to claim 7wherein R is hydroadipic, pirnelic, suberic, azelaic, sebacic,undecanedioic gen and R and R have 1-2 carbon atoms each. anddodecanedioic acids.

9. A diester according to claim 8 wherein R is an 5 alkyl group having4-10 carbon atoms. References Cited 10. A diester according to claim 7wherein R R FOREIGN PATENTS and R have 1-2 carbon atoms each.

11. A diester according to claim 10 wherein R is an M105 2/1961 Francealkyl group having 4-10 carbon atoms. 10 i 12. A diester according toclaim 7 which is a diester HENRY HLESPjzmary i of1-hydroxy-3,5-dimethy1adamantane and an alkanedioic NIELSEN, AsslsfamExamllleracid.

1. A DIESTER HAVING 1-2 ADAMANTANE NUCLEI AND CORRESPONDING TO ONE OF THE FOLLOWING FORMULAS: 